The present invention relates to a sealed encoder for measuring a relative position of two objects movable relative to each other and including a hosing connected with one of the objects and having, in at least one side thereof, a slot extending in a direction of movement of the two objects relative to each other, an entrain member extending in the slot for supporting a position-measuring device and connected with another of the objects, and resilient means extending along the slot for sealing same with the entrain member extending into the slot through the resilient means formed as strip-shaped lips.
Such encoders can be formed as linear or angle encoders functioning in accordance with different physical principles. The encoders are being mounted on different machines for determining a relative position of two or more machine parts.
In sealed encoders, the housing, as known, has a slot into which projects an entrain member that connects a scanning device, located inside the housing, with a mounting block located outside the housing.
When a sealed encoder is used, for example, determining a relative position (movement) of a machine bed and a machine slide movable relative to each other, the relative movement is transferred to the measuring graduation or the scanning device supported by the entrain member, with the entrain member being relatively movable in the movement direction inside the slot.
For protecting the highly sensitive graduation, the housing slot should be sealed as tightly as possible, and the possibility of penetration inside the housing should be provided only in the region of the entrain member.
Such an encoder is shown, e.g., in German Patent No. 2,846,768, in which a scale and a scanning device are located inside a hollow member having a slot extending in a measurement direction. The slot is sealed with sealing elements, which are formed as rubber or plastic lips. The entrain member extends into the inner space of the housing through sealing lips and connects the scanning device with one of the part's relative position or movement of which is measured.
German Patent No. 1,548,871 discloses an encoder in which metallic sealing elements are provided for sealing the housing slot. However, their stiffness is too high to make their adaptation to the entrain member possible.
German Patent No. 3,215,334 discloses an encoder with resilient sealing elements made of a non-metallic material formed of different fibers. This material can include metallic fibers to provide shielding against electromagnetic interference.
German Publication DE 39 30 377A1 discloses a separate sealing element which is arranged between the housing, and associated with the housing cover. This element can be formed of non-metallic material, the outer surface of which is provided with an electroconductive layer.
An object of the invention is a sealed encoder of the above-described type, in which the sealing of the housing slot is effected with mechanically and electrically-resistant sealing elements with an adequate electrical shielding capability.